An electromyographic study of the hip muscles of transfemoral amputees in walking.

The aim of this study was to obtain insight into the electromyographic activity of the hip muscles after transfemoral amputation and to determine whether the cleaved hip muscles are still functional in locomotion. The electromyographic activity of the superficial hip muscles of both legs was studied in 11 men who had a unilateral transfemoral amputation. The intact muscles at the intact and amputated side showed the same sequence of activity as did those in healthy subjects, but during a longer period of time. The activity of the cleaved muscles with intact muscle fibers (gluteus maximus, tensor fasciae latae) was dependent on whether the iliotibial tract was reanchored. If the iliotibial tract was fixed, the same activity was found in the muscles of the patients as in those of healthy subjects. The activity of the cleaved, once biarticular, muscles (sartorius, rectus femoris, hamstring muscles, gracilis) was dependent on whether the muscles were reanchored and on the level of amputation. If the cleaved muscles were reanchored correctly, the muscles remained functional in locomotion in patients with an amputation in the distal half of the femur. In patients with high amputation levels, these muscles were almost continuously active; they probably play a role in fixing the socket.